The instant invention relates to prestressed steel bridge elements which are prefabricated and erected in modular form.
In addition to the normal rate of bridge building, there is a recent accelerated demand to refurbish the nation's highway infrastructure, including replacement of many existing crossings that have fallen into disrepair. There is also a frequent need for quick erection of temporary emergency crossings. Modern bridges are commonly built using one of two methods. The first uses a truss or girder system, typically of structural steel or prestressed concrete beams which are covered by a poured concrete top deck. Another method utilizes poured in place concrete.
Prestressed concrete is well known in building structures of all kinds and typically comprises reinforced concrete which is placed in compression prior to its integration into a structural system, that is, before it starts interacting with the other members of the structure and before loads are introduced. Concrete is frequently prestressed by one of two methods. The pretensioned method involves placing a concrete beam or other member in compression by enclosing pretensioned steel wires within the poured concrete within a mold. A post-tension method of prestressing places the concrete in compression by tensioning the interior cables after the section is cast. Prestressing reduces the amount of concrete required for a given beam or structural member, increases the load-carrying ability of the concrete and reduces load-induced cracking.
More recently, steel structural elements have also been prestressed by the use of cables positioned within the structural profile so as to induce reverse stresses to those which will be occasioned under the normal loads anticipated in the structure. This procedure, however, requires expensive prestressing of the cables and the use of significant attachment points to the steel structure.
Accordingly, it is the primary object of the present invention to provide a modular type prestressed steel bridge beam which can be prefabricated without the use of structural trusses, removable forms or stressing cables.
It is a further object of the instant invention to provide a composite steel-concrete bridge beam which utilizes the weight of a concrete deck for prestressing the steel of which the beam element is constructed without the use of post-tensioned cables or wires.
It is an additional object of the invention to provide a bridge plank or beam which can be easily put in place without the use of cumbersome cranes.
A still further object of the invention is to provide a transport vehicle apparatus for unloading the prefabricated beam of the present invention directly onto bridge abutments.
Other and still further objects, features and advantages of the invention will become apparent from a reading of the following detailed description of a preferred form of the invention taken in connection with the accompanying drawings.